The primary objective of this study is to determine the highest dose of radiation that may be delivered to the lungs using twice daily radiotherapy and three-dimensional treatment planning. Radiation for the treatment of lung cancer is usually given once daily. In this study, the radiation will be given twice-daily to allow for a greater dose of radiation to be delivered in a shorter span of time. Another objective of this study is to test the use of a radiotherapy planning system called three-dimensional conformal planning (3-D). By precisely targeting the tumor while minimizing treatment of normal tissue, it is hoped that tumor control may be improved without increasing side effects.